1. Field of the Invention
The present invention relates to a reduction gear, and more particularly, to a reduction gear that is suitable for a device for driving a joint of an industrial robot.
2. Description of the Related Art
A reduction gear shown in FIG. 6 is disclosed in, for example, in JP-A-2007-285396. The reduction gear 10 includes an input shaft 12, first and second eccentric bodies 14 and 16, first and second externally toothed gears 18 and 20, an internally toothed gear 22, and first and second support flanges 24 and 26 as output members.
The first and second eccentric bodies 14 and 16 have outer peripheries that are eccentric to (not coaxial with) an axis Oi of the input shaft 12, and are formed integrally with the input shaft 12. The eccentric phases of the first and second eccentric bodies 14 and 16 are deviated from each other by 180°. First and second externally toothed gears 18 and 20 are assembled on the outer peripheries of the first and second eccentric bodies 14 and 16.
First and second inner pinholes 40 and 42 are formed at the first and second externally toothed gears 18 and 20. An inner pin 44 and an inner roller 43 penetrate the inner pinholes 40 and 42, and can transmit the rotational components of the first and second externally toothed gears 18 and 20 to first and second support flange.
When the input shaft 12 is rotated by a motor (not shown), the first and second eccentric bodies 14 and 16 are eccentrically rotated together with the input shaft 12 as a single body. Accordingly, if the input shaft 12 is rotated one revolution, the externally toothed gears 18 and 20 assembled on the outer peripheries of the first and second eccentric bodies 14 and 16 oscillate in one time. As a result, the first and second externally toothed gears 18 and 20 are rotated relative to the internally toothed gear 22, which is stopped, by an angle corresponding to the difference in the number of teeth of the first and second externally toothed gears and the internally toothed gear 22. This relative rotation is taken out from any one of the first and second support flanges 24 and 26 through the inner roller 43 and the inner pin 44 as a speed reduction output.
Rollers 34N and 36N without inner and outer rings (or using the first and second eccentric bodies 14 and 16 as inner rings and using the first and second externally toothed gears 18 and 20 as outer rings) are interposed between the outer peripheries of the first and second eccentric bodies 14 and 16 and the first and second externally toothed gears 18 and 20. Further, the input shaft 12 is also supported by rollers 38N and 39N having the same specifications.
The rollers 34N, 36N, 38N, and 39N are fitted to pockets (not shown) with claws of retainers 42, 44, 46, and 48, respectively, so that gaps in a circumferential direction are maintained and the movement of the rollers relative to the retainers 42, 44, 46, and 48 in the axial direction is restricted.
The movement of the retainers 42, 44, 46, and 48 in the axial direction is restricted by thrust washers 60 and 62. Since the movement of the retainers 42, 44, 46, and 48 in the axial direction is restricted by the thrust washers 60 and 62, gaps between the rollers 34N, 36N, 38N, and 39N, which are held in the pockets of the retainers 42, 44, 46, and 48, are maintained in the circumferential direction and the movement of the rollers in the axial direction is restricted at the same time.